In recent years, many digital still cameras which capture still or moving images using image sensors such as CCDs and the like have been developed. These cameras are required to have a multi-pixel structure as they have higher resolutions, higher degrees of freedom in edit, and the like, and the number of pixels of an image sensor is increasing accordingly.
However, the time required to transfer pixels from a photoelectric conversion unit in the order of a vertical transfer path→horizontal transfer path increases with increasing number of pixels, and the time required to capture one still image increases consequently.
For this reason, digital still cameras and the like with a multi-pixel structure are devised to increase the frame rate upon monitoring for field angle adjustment or upon sensing a moving image.
For example, a line decimated read mode is available. This read method improves the frame rate at the cost of the number of pixels/vertical resolution by reading one of every several lines.
As another example, a horizontal pixel addition function is available (e.g., Japanese Patent Laid-Open No. 2000-115643). This read method halves the number of pixels per line by adding every two pixels on an identical line in the horizontal transfer path. With this method, although the number of pixels is halved, the time required to transfer pixels per line can be halved.
Switching of these read methods is implemented by changing the drive timing of a CCD solid-state image sensor.
The conventional image capturing apparatus can improve the frame rate by a devise such as the line decimated read mode upon acquiring a moving image. However, such apparatus must read all pixels/all fields for a still image, and must adopt high-speed drive clocks to take measures against an increase in pixel read time due to the multi-pixel structure and deterioration of consecutive shooting performance accordingly.
When an output image size of the camera is small, a process that applies a signal process by reading pixels more than necessary, and reducing and outputting them in size is required, thus prolonging the time accordingly.
Along with an increase in number of pixels of an image sensor at present and in the future, an application that utilizes a feature of such element which reduces the file size using only a necessary and sufficient image size smaller than that obtained by reading full pixels in addition to a mode of reading all pixels of that image sensor of the camera may increase.